diff --git a/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/AnnotationMethodHandlerAdapter.java b/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/AnnotationMethodHandlerAdapter.java
index 017bc18aeda..8b7f6d95fe3 100644
--- a/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/AnnotationMethodHandlerAdapter.java
+++ b/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/AnnotationMethodHandlerAdapter.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -771,8 +771,8 @@ public class AnnotationMethodHandlerAdapter extends PortletContentGenerator
 			for (RequestMethod method : methods) {
 				this.methods.add(method.name());
 			}
-			this.params = StringUtils.mergeStringArrays(this.params, params);
-			this.headers = StringUtils.mergeStringArrays(this.headers, headers);
+			this.params = PortletAnnotationMappingUtils.mergeStringArrays(this.params, params);
+			this.headers = PortletAnnotationMappingUtils.mergeStringArrays(this.headers, headers);
 		}
 
 		public void initPhaseMapping(String phase, String value, String[] params) {
@@ -782,7 +782,7 @@ public class AnnotationMethodHandlerAdapter extends PortletContentGenerator
 			}
 			this.phase = phase;
 			this.value = value;
-			this.params = StringUtils.mergeStringArrays(this.params, params);
+			this.params = PortletAnnotationMappingUtils.mergeStringArrays(this.params, params);
 		}
 
 		public boolean match(PortletRequest request) {
diff --git a/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/DefaultAnnotationHandlerMapping.java b/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/DefaultAnnotationHandlerMapping.java
index ef792dd0363..b602a2cb3a1 100644
--- a/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/DefaultAnnotationHandlerMapping.java
+++ b/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/DefaultAnnotationHandlerMapping.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -154,7 +154,7 @@ public class DefaultAnnotationHandlerMapping extends AbstractMapBasedHandlerMapp
 					String[] modeKeys = new String[0];
 					String[] params = new String[0];
 					if (typeMapping != null) {
-						params = StringUtils.mergeStringArrays(typeMapping.params(), params);
+						params = PortletAnnotationMappingUtils.mergeStringArrays(typeMapping.params(), params);
 					}
 					ActionMapping actionMapping = AnnotationUtils.findAnnotation(method, ActionMapping.class);
 					RenderMapping renderMapping = AnnotationUtils.findAnnotation(method, RenderMapping.class);
@@ -162,11 +162,11 @@ public class DefaultAnnotationHandlerMapping extends AbstractMapBasedHandlerMapp
 					EventMapping eventMapping = AnnotationUtils.findAnnotation(method, EventMapping.class);
 					RequestMapping requestMapping = AnnotationUtils.findAnnotation(method, RequestMapping.class);
 					if (actionMapping != null) {
-						params = StringUtils.mergeStringArrays(params, actionMapping.params());
+						params = PortletAnnotationMappingUtils.mergeStringArrays(params, actionMapping.params());
 						predicate = new ActionMappingPredicate(actionMapping.name(), params);
 					}
 					else if (renderMapping != null) {
-						params = StringUtils.mergeStringArrays(params, renderMapping.params());
+						params = PortletAnnotationMappingUtils.mergeStringArrays(params, renderMapping.params());
 						predicate = new RenderMappingPredicate(renderMapping.windowState(), params);
 					}
 					else if (resourceMapping != null) {
@@ -183,7 +183,7 @@ public class DefaultAnnotationHandlerMapping extends AbstractMapBasedHandlerMapp
 										Arrays.asList(modeKeys) + " versus " + Arrays.asList(typeMapping.value()));
 							}
 						}
-						params = StringUtils.mergeStringArrays(params, requestMapping.params());
+						params = PortletAnnotationMappingUtils.mergeStringArrays(params, requestMapping.params());
 						if (predicate == null) {
 							predicate = new MethodLevelMappingPredicate(params);
 						}
diff --git a/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/PortletAnnotationMappingUtils.java b/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/PortletAnnotationMappingUtils.java
index f1796355cf4..ac3b6f2dc54 100644
--- a/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/PortletAnnotationMappingUtils.java
+++ b/spring-webmvc-portlet/src/main/java/org/springframework/web/portlet/mvc/annotation/PortletAnnotationMappingUtils.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2009 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,7 +16,9 @@
 
 package org.springframework.web.portlet.mvc.annotation;
 
+import java.util.Arrays;
 import java.util.Iterator;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Set;
 import javax.portlet.ClientDataRequest;
@@ -24,6 +26,7 @@ import javax.portlet.PortletRequest;
 
 import org.springframework.http.MediaType;
 import org.springframework.util.ObjectUtils;
+import org.springframework.util.StringUtils;
 import org.springframework.web.bind.annotation.RequestMethod;
 import org.springframework.web.portlet.util.PortletUtils;
 
@@ -35,6 +38,29 @@ import org.springframework.web.portlet.util.PortletUtils;
  */
 abstract class PortletAnnotationMappingUtils {
 
+	/**
+	 * Merge the given {@code String} arrays into one, with each element only included once.
+	 * <p>The order of elements in the original arrays is preserved (with the exception of
+	 * overlapping elements, which are only included on their first occurrence).
+	 * @param array1 the first array (can be {@code null})
+	 * @param array2 the second array (can be {@code null})
+	 * @return the new array ({@code null} if both given arrays were {@code null})
+	 * @since 4.3.15 (superseding {@link StringUtils#mergeStringArrays})
+	 */
+	public static String[] mergeStringArrays(String[] array1, String[] array2) {
+		if (ObjectUtils.isEmpty(array1)) {
+			return array2;
+		}
+		if (ObjectUtils.isEmpty(array2)) {
+			return array1;
+		}
+
+		Set<String> result = new LinkedHashSet<String>();
+		result.addAll(Arrays.asList(array1));
+		result.addAll(Arrays.asList(array2));
+		return StringUtils.toStringArray(result);
+	}
+
 	/**
 	 * Check whether the given portlet modes matches the specified type-level modes.
 	 * @param modes the mapped portlet modes to check